Check buzzer configuration in **DEVICE/Resources**. You can configure it in a way similar to this:
***percent**: **15**
***period**: *1*
***period**: **1**
Then, put your finger on the [light sensor](http://mangoh.io/uploaded-documents/Reference/mangOH%20Yellow/Discover/HW%20Reference%20Manual/41113116%20mangOH%20Yellow%20HW%20Guide%20-%20HTML5-Responsive%20HTML5/#t=41113116_mangOH_Yellow_HW_Guide_-_HTML5%2FHardware%2FHardware.htm) so that light level value falls below 2.0. After around 15 seconds (and in any case less than 30 seconds), the buzzer starts making a sound.
